1. Field of the Invention
The present invention relates to a process for forming a wear-resistant, sintered layer on a metallic substrate.
2. Description of Prior Art
Conventionally, various proposals have been made for forming a wear-resistant, sintered layer on a metal substrate. For example, Japanese patent publication 53-19540 corresponding to the U.S. Pat. No. 3,743,556 discloses a process for coating a metal substrate with a thin coating composed of filler particles dispersed in a metallic matrix. According to the proposal, there are provided a first layer including filler particles selected from abrasives, metals and alloys and dispersed in an organic binder, and a second layer including a metal or an alloy which has a solidus temperature lower than that of the filler particles and can wet in a molten state the filler particles. The layers are then applied to the substrate and heated to a temperature which is higher than the solidus temperatures of the metal or alloy in the second layer but lower than that of the filler particles whereby the organic binder is dissipated and the filler particles are dispersed in the molten matrix of the metal or alloy in the second layer. According to the process, the filler particles and of relatively large particle size and are not molten during the process so that the original particle size is maintained as it is. Therefore, the substrate having the coating thus produced has a disadvantage of damaging a cooperating surface when it is used as a sliding member.
As an alternative process, it has been proposed to use an alloy powder sheet to form a wear-resistant layer. For example, in Japanese patent application 50-9398 on Jan. 21, 1975 and disclosed for public inspection on July 22, 1976 under the disclosure number 51-83834, there is disclosed a process wherein an alloy particle sheet comprised of alloy particles dispersed in a binder of thermoplastic acryl resin is attached by means of a suitable solvent such as toluene to the metallic substrate and heated in an atmosphere so that a coating of the alloy particles is formed on the substrate. It should however be noted that the process is disadvantageous in that the alloy particles cannot be satisfactorily supported on the substrate in the progress of the process in a temperature wherein the resin binder is dissipated under heat. Thus, when it is desired to form a coating on an inclined surface, a curved surface or a downwardly faced surface, the alloy particles may fall from the substrate during the process. A further problem in the process be is that the alloy sheet has a tendency of shrinking in the sintering process so that there is a difficulty in dimensional control. Thus, it is required to carry out after the sintering process.